Process for the locally restricted etching of a chromium layer

ABSTRACT

A system and process for etching a portion of a chromium layer applied to a substrate is disclosed. The process includes exposing the substrate having the chromium layer to a gas atmosphere containing a halogen compound and an oxygen compound, each of the compounds being selected in such a way that halogen and oxygen radicals are produced, by dissociation induced by electron collisions, at a predetermined rate that is matched to a chromium etching mechanism. An electron beam is directed onto a portion of the substrate that is to be etched.

CROSS-REFERENCE TO RELATED APPLICATIONS

This Utility Patent Application claims priority to German Patent Application No. DE 103 53 591.8, filed on Nov. 17, 2003, which is incorporated herein by reference.

FIELD OF THE INVENTION

The invention relates to a process for etching a portion of a chromium layer which has been applied to a substrate. Moreover, the invention relates to a process for repairing photolithographic masks.

BACKGROUND

When producing microelectronic components, a pattern is transferred from a mask to a semiconductor wafer by means of lithographic imaging. The pattern to be imaged can be represented by opaque and transparent regions in the mask. When producing the mask, a transparent substrate, for example silicon dioxide glass, and a light-absorbing layer, such as chromium, on the substrate are often provided as a mask material. Targeted partial removal of the absorbing material of the layer writes the pattern into the mask, so that the pattern is formed by transparent and opaque regions in the mask.

The partial removal of the absorbing material of the layer can lead to defects on the mask in the form of excess residues of the absorbing material on the transparent regions of the mask. Defects of this nature on the mask are likewise imaged onto the semiconductor wafer and may under certain circumstances interfere with the process of producing a microelectronic component or even make it altogether impossible. Defects on masks are also particularly disadvantageous on account of the fact that a fault caused by the defect is repeated during each further imaging onto the semiconductor wafer and is thereby multiplied.

To enable defective masks to be used, the defects caused by the excess residues of the absorbing material should be removed in a locally restricted manner and with a high positional resolution selectively with respect to the substrate below. It is customary for a chemically enhanced sputter etching step with the aid of a focused gallium ions beam in a bromine atmosphere to be carried out in order to remove excess residues of the absorbing material made from chromium. In this method, the actual removal of material by etching is effected by the momentum of high-energy gallium ions being transmitted to the material that is to be etched, and is therefore physical in nature.

One drawback of predominantly physical etching using the sputter etching method is the relatively low substrate selectivity, which makes it likely that the substrate below will also be partially etched. A further drawback is that high-energy gallium ions are implanted into the transparent substrate. Both partial etching of the substrate and the implantation of the gallium ions into the substrate alter the light-transmitting properties of a defective location, and consequently successful repair is no longer achieved for short exposure wavelengths, such as for example 157 nanometers.

A further process for removing excess residues of the absorbing material on the mask is etching by means of focused electron beams. In this process, an electron beam is directed in a gas atmosphere onto the defective location in the mask. The gas molecules in the gas atmosphere are dissociated in the electron beam, so as to form reactive radicals and ions which react with the absorbing material and etch away material. Since the etching process enhanced by electron beam has virtually no sputtering component, the removal of material by etching is substantially chemical in nature, and consequently it is possible to achieve a high substrate selectivity. Moreover, this etching process does not cause any foreign atoms to be implanted into the substrate. On account of the improved focusing properties of electron beams compared to ion beams, a higher positional resolution is also achieved with the aid of focused electron beams, which is advantageous in particular in view of the ever decreasing feature sizes.

However, the electron beam enhanced etching process can at present only be used to etch light-absorbing materials, such as MoSiN and TaN. Attempts to use this process to etch an absorbing material such as chromium which is often used have hitherto proven unsuccessful.

SUMMARY

Embodiments of the invention provide a system and process for etching a portion of a chromium layer applied to a substrate, suitable for use in repairing mask defects, in a photolithographic imaging operation. In one embodiment, the method includes exposing the substrate having the chromium layer to a gas atmosphere containing a halogen compound and an oxygen compound, each of the compounds being selected in such a way that halogen and oxygen radicals are produced, by dissociation induced by electron collisions, at a predetermined rate that is matched to a chromium etching mechanism directing an electron beam onto a portion of the substrate that is to be etched.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings are included to provide a further understanding of the present invention and are incorporated in and constitute a part of this specification. The drawings illustrate the embodiments of the present invention and together with the description serve to explain the principles of the invention. Other embodiments of the present invention and many of the intended advantages of the present invention will be readily appreciated as they become better understood by reference to the following detailed description. The elements of the drawings are not necessarily to scale relative to each other. Like reference numerals designate corresponding similar parts.

FIG. 1 illustrates a diagrammatic exemplary embodiment of an arrangement for etching a chromium layer in accordance with the invention.

DETAILED DESCRIPTION

In the following Detailed Description, reference is made to the accompanying drawings, which form a part hereof, and in which is shown by way of illustration specific embodiments in which the invention may be practiced. In this regard, directional terminology, such as “top,” “bottom,” “front,” “back,” “leading,” “trailing,” etc., is used with reference to the orientation of the Figure(s) being described. Because components of embodiments of the present invention can be positioned in a number of different orientations, the directional terminology is used for purposes of illustration and is in no way limiting. It is to be understood that other embodiments may be utilized and structural or logical changes may be made without departing from the scope of the present invention. The following detailed description, therefore, is not to be taken in a limiting sense, and the scope of the present invention is defined by the appended claims.

The present invention provides a process that allows electron beam enhanced etching of chromium. The object invention encompasses a process for repairing a mask for lithographic imaging operations.

In one embodiment, the invention provides a process for etching a portion of a chromium layer which has been applied to a substrate. In the process, the substrate which bears the chromium layer is exposed to a gas atmosphere containing a halogen and oxygen, in each case in the form of compounds. According to one embodiment of the invention, the compounds are selected in such a way that halogen and oxygen radicals are in each case produced, by dissociation induced by electron collisions, at a rate which is matched to a chromium etching mechanism. An electron beam is directed onto the portion that is to be etched. Halogen and oxygen radicals are produced as a result of dissociation, induced by electron collisions, of the compounds in the electron beam in accordance with the invention at the respectively predetermined rate, and chromium is reacted with oxygen and chlorine radicals, on account of the rates in each case being matched to the chromium etching mechanism, to form a volatile compound.

The chromium etching mechanism consists in reacting chromium with oxygen and halogen radicals to form a volatile compound containing chromium, oxygen and the halogen. It seems probable that the conventional approach using a Cl₂/O₂ gas atmosphere failed on account of the dissociation rate induced by electron collisions of the oxygen molecule being significantly lower than that of the chlorine. According to one embodiment of the invention, this problem is solved by the use of compounds in which halogen and oxygen radicals are produced by dissociation induced by electron collisions in each case at a rate which is matched to the chromium etching mechanism. The use of suitable halogen- and oxygen-containing compounds advantageously also allows the electron beam enhanced etching process to be used for locally restricted removal of chromium.

It is preferable in one embodiment for molecular chlorine Cl₂ and an oxygen-containing compound with a dissociation rate induced by electron collisions which is matched to the dissociation rate induced by electron collisions of the Cl₂ are provided for the compounds. To enable chromium to be converted into the volatile compound chromyl chloride CrO₂Cl₂ oxygen and chlorine radicals should be present in similar levels or with more oxygen radicals than chlorine radicals. This is achieved by selecting an oxygen-containing compound with a dissociation rate which is downgraded to the dissociation rate of Cl₂. It is preferably for water H₂O or nitrogen oxides N_(x)O_(y) to be used for the oxygen-containing compound.

Dinitrogen oxide N₂O is advantageously used for the oxygen-containing compound. N₂O is easier to dissociate than molecular oxygen.

It is preferable for Cl₂ and N₂O to be provided in the gas atmosphere in a ratio in a range between 10:1 and 1:10. The gas pressure is in this case provided in a range between 10⁻⁴ and 10⁻⁸ mbar.

It is preferable for Cl₂ and chlorine oxides Cl_(x)O_(y), or Cl₂ and chlorine acids HClO_(x) to be provided for the compounds.

It is preferable for a chlorine- and oxygen-containing compound to be provided in the gas atmosphere.

It is preferable for a chlorine oxide Cl_(x)O_(y) or a chlorine acid HClO_(x) to be provided for the compound.

In one embodiment, the invention also provides a process for repairing defects on masks caused by locally restricted chromium residues on transparent regions. The masks for lithographic imaging of a pattern from the mask onto a semiconductor wafer are provided with opaque regions provided from chromium and transparent regions forming the pattern. According to one embodiment of the invention the locally restricted chromium residues correspond to the abovementioned portion and the transparent regions of the mask correspond to the abovementioned substrate. The defect on the mask caused by the chromium residues is repaired by means of the described process for etching the portion of a chromium layer. The advantage of this process for repairing masks is that microscopically small chromium residues can be removed in a strictly locally restricted manner and selectively with respect to the transparent region of the mask below. Moreover, this process avoids damage caused by high-energy ions being implanted in the transparent region. The repair yield with the aid of the electron beam enhanced etching process is significantly increased compared to conventional repair processes by means of a gallium ion beam. Since the production of masks is technically highly complex and cost-intensive, the use of the electron beam enhanced etching process in mask repair means a significant improvement over the prior art with regard to defects caused by chromium residues.

FIG. 1 illustrates a substrate 1 on which there is arranged a chromium layer 2 with a portion 3 that is to be removed. An electron beam 6, which is focused by means of electromagnetic fields in an electron beam gun 5, is directed onto the portion 3. There is a gas inlet 4 in the vicinity of the electron beam 6. A gas which generates a gas atmosphere is admitted through the gas inlet 4. The gas contains chlorine- and oxygen-containing compounds which are dissociated in the electron beam 6. The chlorine- and oxygen-containing compounds are selected in such a way that chlorine radicals and oxygen radicals are generated at a rate which is matched to the chromium etching mechanism as a result of dissociation, induced by electron collisions, of the compounds in the electron beam 6. The radicals generated by the focused electron beam 6 react with the chromium of the portion 3 and form a volatile chromyl chloride CrO₂Cl₂. The chemical conversion of chromium into volatile chromyl chloride is responsible for the removal of material by etching.

The described process for etching the portion 3 of the chromium layer 2 which is arranged on a substrate 1 can particularly advantageously also be used to repair photolithographic masks. In the mask, a pattern which is to be imaged by means of a photolithographic process is represented by opaque regions and transparent regions of the mask. To produce the mask, an opaque chromium layer is applied to a transparent carrier material, which corresponds to the substrate 1 and may be a silicon dioxide, and is patterned in such a way that the mask has transparent and opaque regions. Defects formed during the production of masks may be caused, inter alia, by chromium residues remaining on transparent regions. The above-described process according to the invention is particularly suitable for removing these chromium residues, which correspond to the portion 3 in FIG. 1, on the transparent regions which correspond to the substrate 1 in FIG. 1. The focused electron beam 6 advantageously carries out etching attack with a high positional resolution. This is important in particular in connection with the ongoing reduction in feature sizes. Since, moreover, the actual removal of material by etching is purely chemical in nature, it is possible to achieve a good selectivity with respect to the material below, which is advantageous in particular for a mask repair, in which the transparent regions must not experience any damage.

Although specific embodiments have been illustrated and described herein, it will be appreciated by those of ordinary skill in the art that a variety of alternate and/or equivalent implementations may be substituted for the specific embodiments shown and described without departing from the scope of the present invention. This application is intended to cover any adaptations or variations of the specific embodiments discussed herein. Therefore, it is intended that this invention be limited only by the claims and the equivalents thereof. 

1. A process for etching a portion of a chromium layer applied to a substrate in which: exposing the substrate having the chromium layer to a gas atmosphere containing a halogen compound and an oxygen compound, each of the compounds being selected in such a way that halogen and oxygen radicals are produced, by dissociation induced by electron collisions, at a predetermined rate that is matched to a chromium etching mechanism; and directing an electron beam onto a portion of the substrate that is to be etched.
 2. The process of claim 1, wherein halogen radicals and oxygen radicals are produced as a result of the dissociation, induced by electron collisions, of the compounds in the electron beam at the respectively predetermined rate, and chromium is reacted with oxygen and halogen radicals, on account of the rates in each case being matched to the chromium etching mechanism, to form a volatile compound.
 3. The process of claim 2, wherein molecular chlorine Cl₂ and an oxygen-containing compound with a dissociation rate induced by electron collisions that is matched to the dissociation rate induced by electron collisions of the Cl₂ are provided for the compounds; and chromium is reacted with oxygen and chlorine radicals to form volatile chromyl chloride CrO₂Cl₂.
 4. The process of claim 3, wherein water H₂O, or nitrogen oxides N_(x)O_(y) are used for the oxygen-containing compound.
 5. The process of claim 3, wherein dinitrogen oxide N₂O is used for the oxygen-containing compound.
 6. The process as claimed in claim 5, comprising: providing Cl₂ and N₂O in the gas atmosphere in a ratio in a range between 10:1 and 1:10; and providing the gas pressure in a range between 10⁻⁴ and 10⁻⁸ mbar.
 7. The process of claim 1, comprising providing Cl₂ and chlorine oxides Cl_(x)O_(y), or Cl₂ and chlorine acids HClO_(x) for the compounds.
 8. The process of claim 1, comprising providing a chlorine-containing and oxygen-containing compound in the gas atmosphere.
 9. The process of claim 7, comprising providing a chlorine oxide Cl_(x)O_(y) or a chlorine acid HClO_(x) as the compound.
 10. A process for repairing defects, caused by locally restricted chromium residues on transparent regions of a substrate, on masks having the opaque regions provided from chromium and transparent regions forming a pattern for lithographic imaging of the pattern from the mask onto a semiconductor wafer, comprising: exposing the substrate having the chromium residue to a gas atmosphere containing a halogen compound and an oxygen compound, each of the compounds being selected in such a way that halogen and oxygen radicals are produced, by dissociation induced by electron collisions, at a predetermined rate that is matched to a chromium etching mechanism; and directing an electron beam onto the chromium residue on the substrate.
 11. The process of claim 10, wherein halogen radicals and oxygen radicals are produced as a result of the dissociation, induced by electron collisions, of the compounds in the electron beam at the respectively predetermined rate, and chromium residue is reacted with oxygen and halogen radicals, on account of the rates in each case being matched to the chromium etching mechanism, to form a volatile compound.
 12. The process of claim 11, wherein molecular chlorine Cl₂ and an oxygen-containing compound with a dissociation rate induced by electron collisions that is matched to the dissociation rate induced by electron collisions of the Cl₂ are provided for the compounds; and chromium is reacted with oxygen and chlorine radicals to form volatile chromyl chloride CrO₂Cl₂.
 13. The process of claim 12, wherein water H₂O, or nitrogen oxides N_(x)O_(y) are used for the oxygen-containing compound.
 14. The process of claim 13, wherein dinitrogen oxide N₂O is used for the oxygen-containing compound.
 15. The process as claimed in claim 14, comprising: providing Cl₂ and N₂O in the gas atmosphere in a ratio in a range between 10:1 and 1:10; and providing the gas pressure in a range between 10⁻⁴ and 10⁻⁸ mbar.
 16. The process of claim 11, comprising providing Cl₂ and chlorine oxides Cl_(x)O_(y), or Cl₂ and chlorine acids HClO_(x) for the compounds.
 17. The process of claim 11, comprising providing a chlorine-containing and oxygen-containing compound in the gas atmosphere.
 18. A process for etching a portion of a chromium layer applied to a substrate in which: exposing the substrate having the chromium layer to a gas atmosphere containing a halogen compound and an oxygen compound, each of the compounds being selected in such a way that halogen and oxygen radicals are produced, by dissociation induced by electron collisions, at a predetermined rate that is matched to a chromium etching mechanism; and directing an electron beam onto a portion of the substrate that is to be etched, wherein halogen radicals and oxygen radicals are produced as a result of the dissociation, induced by electron collisions, of the compounds in the electron beam at the respectively predetermined rate, and chromium is reacted with oxygen and halogen radicals, on account of the rates in each case being matched to the chromium etching mechanism, to form a volatile compound, and wherein molecular chlorine Cl₂ and an oxygen-containing compound with a dissociation rate induced by electron collisions that is matched to the dissociation rate induced by electron collisions of the Cl₂ are provided for the compounds; and chromium is reacted with oxygen and chlorine radicals to form volatile chromyl chloride CrO₂Cl₂.
 19. The process of claim 18, wherein water H₂O, or nitrogen oxides N_(x)O_(y) are used for the oxygen-containing compound.
 20. The process of claim 18, wherein dinitrogen oxide N₂O is used for the oxygen-containing compound, and providing Cl₂ and N₂O in the gas atmosphere in a ratio in a range between 10:1 and 1:10; and providing the gas pressure in a range between 10⁻⁴ and 10⁻⁸ mbar.
 21. A process for etching a portion of a chromium layer applied to a substrate comprising: means for exposing the substrate having the chromium layer to a gas atmosphere containing a halogen compound and an oxygen compound, each of the compounds being selected in such a way that halogen and oxygen radicals are produced, by dissociation induced by electron collisions, at a predetermined rate that is matched to a chromium etching mechanism; and means for directing an electron beam onto a portion of the substrate that is to be etched.
 22. The process of claim 21, wherein halogen radicals and oxygen radicals are produced as a result of the dissociation, induced by electron collisions, of the compounds in the electron beam at the respectively predetermined rate, and chromium is reacted with oxygen and halogen radicals, on account of the rates in each case being matched to the chromium etching mechanism, to form a volatile compound, wherein molecular chlorine Cl₂ and an oxygen-containing compound with a dissociation rate induced by electron collisions that is matched to the dissociation rate induced by electron collisions of the Cl₂ are provided for the compounds; and chromium is reacted with oxygen and chlorine radicals to form volatile chromyl chloride CrO₂Cl₂.
 23. A system for etching a portion of a chromium layer applied to a substrate in which: a gas configured to expose the substrate having the chromium layer to a gas atmosphere containing a halogen compound and an oxygen compound, each of the compounds being selected in such a way that halogen and oxygen radicals are produced, by dissociation induced by electron collisions, at a predetermined rate that is matched to a chromium etching mechanism; and an electron beam focused onto a portion of the substrate that is to be etched.
 24. The system of claim 23, wherein halogen radicals and oxygen radicals are produced as a result of the dissociation, induced by electron collisions, of the compounds in the electron beam at the respectively predetermined rate, and chromium is reacted with oxygen and halogen radicals, on account of the rates in each case being matched to the chromium etching mechanism, to form a volatile compound.
 25. The process of claim 24, wherein molecular chlorine Cl₂ and an oxygen-containing compound with a dissociation rate induced by electron collisions that is matched to the dissociation rate induced by electron collisions of the Cl₂ are provided for the compounds; and chromium is reacted with oxygen and chlorine radicals to form volatile chromyl chloride CrO₂Cl₂.
 26. The system of claim 23, comprising: a gas inlet positioned proximate the substrate, wherein the gas is provided via the gas inlet. 